Method of transmitting ethernet frame in network bridge and the bridge

ABSTRACT

Provided is a method of transmitting an Ethernet frame via a network bridge, the method includes receiving a frame header from a previous node connected to the network bridge; receiving a header cyclic redundancy check (CRC) flag and header CRC with respect to the frame header from the previous node; determining whether to forward the Ethernet frame including the frame header by referring to the header CRC flag and the header CRC; and forwarding the Ethernet frame from the previous node to a next node connected to the network bridge according to the determination.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/591,591, filed on Nov. 2, 2006, which claims the benefitunder 35 U.S.C.§119(a) of Korean Patent Application No. 10-2006-0059782,filed on Jun. 29, 2006, in the Korean Intellectual Property Office, theentire disclosure of each of which is hereby incorporated by referencefor all purposes.

BACKGROUND

1. Field

The following disclosure relates to a method of transmitting an Ethernetframe in a network bridge. More particularly, the following disclosurerelates to a method of transmitting a frame using a check-and-forwardtechnique by using a header CRC flag included in a received Ethernetframe and header CRC.

2. Description of the Related Art

Development of computer network technologies for the Internet has leadto the development of technologies for the general information industry.The developed network technologies opens up new vistas of computingtechnology, such as providing new services that generate added value towired or wireless connections between computers.

Network technologies have been rapidly developed and now virtually allcomputers are connected to a network. Ethernet is an essential aspect ofthe success of network technologies. Ethernet has been used in numeroustypes of wired/wireless networks, due to its simple structure.

However, despite Ethernet having been applied to broad fields, Ethernethas not been generally used in time-sensitive and real-time streamingapplications, due to a limit of being incapable of supportingisochronous services. Due to a rapid increase of interests inhigh-quality digital audio-video services, the above limit of theEthernet has increasingly gained attention. Currently, starting withresidential Ethernet, research on Ethernet technology for supportingtime-sensitive applications is vigorously being pursued.

A network bridge is an apparatus for transmitting an Ethernet framebetween nodes mutually connected via a network. A conventional Ethernetnetwork bridge apparatus supports a frame transmission method generallyreferred to as a store-and-forward technique. The store-and-forwardtechnique has a switching method in which an entire received Ethernetframe is temporarily stored in a buffer and is forwarded to a next nodeafter a process of detecting an error, such as cyclic redundancy check(CRC), is finished.

Since a considerable amount of time is used in receiving and storing anEthernet frame and a delay at each node is added to an end-to-end delay.Thus, the above switching method is not suitable for the time-sensitiveapplications.

Conversely, to solve the problem of excessive delays of thestore-and-forward technique, when using a cut-through switchingtechnique in which a frame is directly forwarded by referring to aheader of a received Ethernet frame, data included in the frame header,such as a destination address, a source address, and a frame type, isnot reliable.

Accordingly, a switching method is needed to secure precision of theframe header data while reducing a time delay due to the forwarding ofthe frame to support a real-time application.

Also, in a future home network to which real-time applications areapplied, digital rights management (DRM) for provided content is animportant issue. In one implementation of the DRM, repeated use ofcontent with respect to some applications is limited to a local scope,such as residential scope. In this case, a media server of a contentprovider has to recognize whether a media player of a content receiveris located within a scope of a certain network distance from a sender ofdata. However, since a conventional Ethernet bridge apparatus does notsupport a network distance measurement and a time delay at a bridgeapparatus forming each node has a great variance depending upon atraffic state, it is difficult to precisely measure.

SUMMARY

Embodiments provide a network bridge apparatus capable of solving theabove problems, effectively supporting time-sensitive and real-timeapplications, and maintaining compatibility with a conventional Ethernetbridge apparatus.

An aspect of example embodiments is to address at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of example embodiments providesa network bridge apparatus suitable for supporting a time-sensitiveapplication and a method of transmitting an Ethernet frame by using thenetwork bridge apparatus.

An aspect of example embodiments also provides a frame transmissionmethod capable of satisfying a time delay of a low level required in areal-time application, by securing precision of data of an Ethernetframe header via a cyclic redundancy check (CRC) header using a headerCRC flag included in the Ethernet frame and a header CRC, as well asselectively performing a CRC on an entirety of the Ethernet frame.

An aspect of example embodiments also provides a frame transmissionmethod in which, a function of precisely measuring a distance between acontent provider and a content receiver on a network is supported byforwarding a distance measurement frame with a top priority.Accordingly, digital rights management (DRM) with respect to contentsprovided in real-time may be effectively supported.

An aspect of example embodiments also provides a network bridgeapparatus effectively supporting an additional function associated withreal-time applications as well as maintaining compatibility with aconventional Ethernet bridge and securing flexibility and expandabilityof an Ethernet network via the example embodiments.

An aspect of example embodiments also provides a network bridgeapparatus in which a state transition counter is compared with athreshold determined by probability computation to make a transition ofa state, thereby forwarding a frame more reliably.

According to an aspect of example embodiments, there is provided amethod of transmitting an Ethernet frame via a network bridge, themethod including: receiving a frame header from a previous nodeconnected to the network bridge; receiving a header cyclic redundancycheck (CRC) flag and header CRC with respect to the frame header fromthe previous node; determining whether to forward the Ethernet frameincluding the frame header by referring to the header CRC flag and theheader CRC; and forwarding the Ethernet frame from the previous node toa next node connected to the network bridge according to thedetermination.

According to another aspect of example embodiments, there is provided amethod of transmitting an Ethernet frame via a network bridge, themethod including: receiving the Ethernet frame from a previous node;verifying whether the Ethernet frame is a distance measurement frame formeasuring a network distance between a sender and a receiver, byreferring to a header of the Ethernet frame; and forwarding the distancemeasurement frame with a top priority when the Ethernet frame isverified to be the distance measurement frame as a result of theverification.

According to still another aspect of example embodiments, there isprovided a network bridge apparatus transmitting an Ethernet frame, thenetwork bridge including: a frame receiving unit receiving the Ethernetframe from a previous node connected to the network bridge; a CRC unitperforming a CRC with respect to a header of the Ethernet frame by usinga header CRC flag and a header CRC included in the Ethernet frame, orperforming the CRC with respect to an entirety of the Ethernet frame byusing a CRC field of the Ethernet frame; a state management unitdetermining an operation state of the network bridge according to aresult of the CRC; and a frame transmission unit discarding the receivedframe or transmitting the received frame to a next node by referring tothe operation state and the result of the CRC.

Other features and aspects may be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of an Ethernet frameaccording to an example embodiment.;

FIG. 2 is a diagram illustrating a configuration of an Ethernet networkincluding a network bridge apparatus according to an example embodiment.

FIG. 3 is a flowchart illustrating a method of transmitting an Ethernetframe, according to an example embodiment.

FIG. 4 is a flowchart illustrating an operation of forwarding a frame,illustrated in FIG. 3, in detail.

FIG. 5 is a block diagram illustrating an internal configuration of anetwork bridge apparatus according to an example embodiment.

FIG. 6 is a diagram illustrating transition between states maintainedand determined by a state management unit.

FIG. 7 is a flowchart illustrating operations of a frame transmissionunit illustrated in FIG. 5, distinguished according to a state, whethera header CRC flag is valid, and a value of the header CRC flag.

FIG. 8 is a flowchart illustrating operations when the frametransmission unit illustrated in FIG. 7 transmits an Ethernet framewhose header CRC flag value is ON in a first state.

FIG. 9 is a flowchart illustrating operations when the frametransmission unit illustrated in FIG. 7 transmits an Ethernet framewhose header CRC flag value is OFF in the first state.

FIG. 10 is a flowchart illustrating operations when the frametransmission unit illustrated in FIG. 7 transmits an Ethernet frameincluding an invalid header CRC flag in the first state.

FIG. 11 is a flowchart illustrating operations when the frametransmission unit illustrated in FIG. 7 transmits an Ethernet frameincluding a valid header CRC flag in a second state.

FIG. 12 is a flowchart illustrating operations when the frametransmission unit illustrated in FIG. 7 transmits an Ethernet frameincluding an invalid header CRC flag in the second state.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals should be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. Accordingly, various changes,modifications, and equivalents of the systems, apparatuses and/ormethods described herein will be suggested to those of ordinary skill inthe art. The progression of processing steps and/or operations describedis an example; however, the sequence of steps and/or operations is notlimited to that set forth herein and may be changed as is known in theart, with the exception of steps and/or operations necessarily occurringin a certain order. Also, descriptions of well-known functions andconstructions may be omitted for increased clarity and conciseness.

FIG. 1 is a diagram illustrating a configuration of an Ethernet frame100 according to an example embodiment. The Ethernet frame 100 includesa header 120, a payload 130, and a frame check sequence (FCS) 140.

Also, although not included in the Ethernet frame 100, there is apreamble 110 in the front of the frame header 120 to be used fordetecting a frame signal received at a physical layer. The preamble 110generally includes 7 bytes, and a function of the preamble 110, withrespect to an example embodiment, will be described later.

The payload 130 is the part of the Ethernet frame 100 that stores realdata and it does not include overhead for use or control of the Ethernetframe 100. As shown in FIG. 1, the payload 130 includes a header CRCflag (HCRCF) and a header CRC (HCRC). The HCRC is CRC bits with respectto the frame header 120, and the HCRCF is an indicator indicatingwhether to perform CRC on the frame header 120 by using the HCRC.

Conversely, the FCS 140 includes information for detecting an error inthe entire Ethernet frame. For example, the FCS 140 may include CRC bitsfor the entire Ethernet frame. Accordingly, in an example embodiment,“CRC of the entire Ethernet frame” or “CRC of the Ethernet frame”indicates a process of detecting an error within the Ethernet frame byusing the CRC bits stored in the FCS 140 located at an end of theEthernet frame 100, or indicates a result of an error detection.

A network bridge apparatus according to an example embodiment receivesthe frame first and receives the HCRCF and the HCRC. The bridgeapparatus determines the Ethernet frame 100 is to be associated with areal-time application when a value of a header CRC flag is ON andperforms an operation of forwarding to reduce a time delay. The bridgeapparatus performs CRC on the frame header 120 by using the HCRC. Whenthere is no data error in the frame header as determined by the CRC, thebridge apparatus transmits the Ethernet frame 100 to the next node viaan output port. Here, the transmitted Ethernet frame 100 was inputbefore the payload 130 was completely received and includes a datafield. When there is a data error in the frame header 120, the Ethernetframe 100 is not transmitted to the next node and is instead discarded.As described above, an example embodiment provides a frame transmissionmethod of a check-and-forward technique in which the CRC on the frameheader 120 is performed by using the HCRCF and HCRC. Forwarding of theframe is immediately started without storing an inputted frame whenthere is no data error.

Conversely, when a value of the HCRCF is OFF, the bridge apparatusdetermines the inputted Ethernet frame 100 to be a general Ethernetframe and transmits the Ethernet frame 100 to the next node according toa store-and-forward technique. The entire inputted Ethernet frame 100 isreceived and stored in a buffer and the CRC on the entire Ethernet frame100 is performed by using the CRC bits of the Ethernet frame 100. Whenthere is no data error in the Ethernet frame 100 as determined by theCRC, the Ethernet frame 100 is transmitted to the next node via theoutput port. When there is a data error in the Ethernet frame 100 asdetermined by the CRC, the Ethernet frame 100 is discarded.

The above frame transmission method of the check-and-forward techniqueaccording to an example embodiment is a switching method optimized forreal-time applications.

Since the check-and-forward technique determines whether to forward ordiscard by performing the CRC on the frame header 120 instead ofperforming the CRC on the entire Ethernet frame 100, the operation offorwarding is performed quickly. The check-and-forward technique isbeneficial with respect to the real-time applications that require aquick frame forwarding process. Also, when it is determined whether ornot to forward, frame bits inputted before receiving the entire Ethernetframe 100 are directly transferred to the output port and transmitted tothe next node. Thereby, transmission speed of the Ethernet frame 100 ina network is improved.

In a real-time application, when the payload 130 includes a data error,the entire Ethernet frame 100, including the payload 130, may betransmitted with the error instead of discarding or retransmitting theentire Ethernet frame 100. Namely, in a real-time streaming application,timeliness may be a more important variable than data precision.

Accordingly, in the check-and-forward technique, with respect to a framewhose value of HCRCF is ON, namely, the Ethernet frame 100 associatedwith a real-time application, regardless of whether there is an error inthe entire Ethernet frame 100, when there is no error in the frameheader 120, the entire Ethernet frame 100 is forwarded to the next node.

Also, according to the configuration of the Ethernet frame 100,illustrated in FIG. 1, the HCRCF and HCRC are included in the payload130 instead of added as an additional header, thereby maintaining auniform size for the entire Ethernet frame 100. Particularly, since theheader CRC flag and the header CRC associated with the check-and-forwardoperation are located in the front of the payload 130, it is quicklydetermined at a beginning whether to store the rest of data field of thepayload 130 in a buffer so as to prevent an unnecessary time delay.

For reference, when the HCRCF and the HCRC occupy 1 byte, respectively,to make the HCRCF and the HCRC included in the payload 130 as shown inFIG. 1, it is required to assume that data stored in the payload 130 isnot more than 1498 bytes because 1500 bytes is a maximum payload size.Though most real-time applications may be expected to satisfy the aboveassumption, when a frame including 1500 bytes and requiring real-timeprocessing is inputted and has to be transmitted by using thecheck-and-forward technique, the HCRCF and the HCRC may be included inthe preamble 110 associated with the Ethernet frame 100 instead of thepayload 130.

As described above, the preamble 110 is a field for storing data that isused for detecting a received signal. The preamble 110 includes 7 bytesin the front of the frame header 120. While all 7 bytes of the preamble110 for signal detection are conventionally used, using all 7 bytes ofthe preamble 110 for signal detection is now considered to consume anexcessive amount of traffic resources, due to development of thephysical layer technology.

Accordingly, a part of the preamble 110 is used for storing the HCRCFand the HCRC, according to an example embodiment. According to thepresent example embodiment, a node receiving an Ethernet frame requiringreal-time processing receives a HCRCF and HCRC field stored in 2 bytesof the 7 bytes of the preamble 110 first. The frame header 120 of theEthernet frame is received, and the Ethernet frame is transmitted by thecheck-and-forward technique by using the HCRCF and HCRC extracted fromthe preamble 110.

A Type/Length field located in the front of the frame header 120 is usedfor identifying a distance measurement frame according to anotherexample embodiment. The identification of the distance measurement frameis performed before transmission in the check-and-forward technique.Accordingly, the node receiving the Ethernet frame 100 receives thetype/length field of the frame header 120 first, checks whether theEthernet frame 100 is the distance measurement frame, and receives therest of the frame header 120 to perform the transmission in thecheck-and-forward technique by using the HCRCF and HCRC when theEthernet frame 100 is not the distance measurement frame, and is areal-time frame requiring the transmission in the check-and-forwardtechnique.

FIG. 2 is a diagram illustrating a configuration of an Ethernet networkincluding a network bridge apparatus operating according to an exampleembodiment. A residential Ethernet network is an example of the aboveEthernet network.

Referring to FIG. 2, a routing path 201 includes bridge apparatus 211and bridge apparatus 221 that are two edge nodes of the local Ethernetnetwork. Routing path 201 illustrates the transmission of real-timeaudio or video data from an application of bridge apparatus 211 to anapplication of bridge apparatus 221.

Conversely, a routing path 202 illustrates an Ethernet frame transmittedfrom an external network to an application of bridge apparatus 222 via abridge apparatus 212 that is an edge node of the local Ethernet networkand intermediate nodes.

As shown in the routing paths 201 and 202, a bridge apparatus supportinga check-and-forward function may be used together with a bridgeapparatus that does not support the check-and-forward function on anetwork. Accordingly, the frame transmission method according to anexample embodiment includes operations that maintain compatibility witha conventional network bridge apparatus as well as providing an improvedswitching function via the check-and-forward function.

FIG. 3 is a flowchart illustrating a method of transmitting an Ethernetframe, according to an example embodiment. Referring to FIG. 3, inoperations S310 and S320, a frame header and a HCRCF and HCRC arereceived, respectively. A node connected to a port receiving the frameis called a previous node. In operation S325, it is determined if thevalue of the HCRCF is “on”.

If the value of the HCRCF is “on”, in operation S330, a CRC on the frameheader is performed. In operation S335, it is determined if the resultof the CRC indicates an error. When there is no CRC error, bits of thereceived frame are forwarded prior to receiving an entire frame inoperation S340. When there is a CRC error, the frame is not forwarded toa next node but is discarded in operation S350. In this case, the nextnode is a node connected to an output port, to which a frame istransmitted.

For reference, the previous node and the next node in the network bridgeapparatus are determined according to the direction of transmission ofan Ethernet frame. Specifically, the previous node is a node connectedto a port that receives the Ethernet frame and the next node is a nodeconnected to a port that transmits the Ethernet frame. Since the networkbridge apparatus supports a bidirectional packet flow, positions of theprevious node and the next node may be mutually changed according to thedirection of the transmission of the frame.

Conversely, when the value of the HCRCF is “off” in operation S325, thebridge apparatus operates in the store-and-forward technique, asdescribed above. Accordingly, in operation S360, the entire Ethernetframe is received and stored. After completion of storage, the receivedEthernet frame is forwarded to the next node in operation S340.

As described above, the network bridge apparatus supporting thecheck-and-forward technique may be used together with the bridgeapparatus that does not support the function. Accordingly, the networkbridge apparatus determines whether the previous node and the next nodesupports the check-and-forward technique, respectively, and processesthe frame to be transmitted so as to be in a suitable form according tothe determination.

FIG. 4 is a flowchart illustrating different operations of forwarding aframe S340, wherein the operation chosen to forward the frame dependsupon whether the previous node and the next node support thecheck-and-forward technique. For reference, the term “supporting thecheck-and-forward technique” used below indicates that the HCRCF and theHCRC included in a payload may be identified.

Referring to FIG. 4, operation S340 of forwarding the Ethernet frameincludes sub-operation S341 of verifying whether the previous node andthe next node support the check-and-forward technique. When the previousnode and the next node support the check-and-forward technique asdetermined by the verification, in sub-operation S342, the receivedframe is forwarded as is, without an additional process.

However, when the previous node does not support the check-and-forwardtechnique, the HCRCF and the HCRC are not included in a payload of thereceived frame. In this case, when the next node also does not supportthe check-and-forward technique, and the received frame is forwardedwithout adding the HCRCF and the HCRC. When the next node supports thecheck-and-forward technique, to prevent a malfunction at the next node,at least the HCRCF is inserted into the received frame to betransmitted. In this case, since the received frame does not include theHCRCF and the HCRC, performing a CRC on a frame header by the next nodeis meaningless. Accordingly, a value of the HCRCF inserted in to theforwarded frame is established as “off” in operation S343.

Conversely, when the next node does not support the check-and-forwardtechnique, the forwarded frame does not include the HCRCF and the HCRC,regardless of whether the previous node supports the check-and-forwardtechnique. When the previous node supports the check-and-forwardtechnique, the HCRCF and HCRC are removed from the received frame. Whenthe previous node does not support the check-and-forward technique, thereceived frame is forwarded without adding the HCRCF and HCRC. Since aprocess of forwarding a frame may be considered as a process ofreceiving the frame and transmitting a frame formed of bits having anidentical value with bits of the received frame, in the detaileddescription, the claims, and the drawings of the present specification,the two cases are expressed as “removing the HCRCF and the HCRC”. Theabove process is illustrated in operation S344.

Also, although not shown in FIG. 3, the frame transmission methodaccording to an example embodiment may include an operation of verifyingwhether an Ethernet frame including a frame header is a distancemeasurement frame by referring to the frame header, immediately afteroperation S310 of receiving a frame header. In an example embodiment,“the distance measurement frame” indicates a distance between a sendersending an Ethernet frame and a receiver receiving the Ethernet frame ona network and may include a ping frame sent from the sender to thereceiver and a responsive ping frame sent from the receiver to thesender.

The sender measures a round-trip time from a point in time of sendingthe ping frame to a point in time of receiving the responsive pingframe, thereby measuring a network distance between the sender and thereceiver. Here, network distance may also be a network latency. In thiscase, whether the frame is the distance measurement frame such as theping frame or the responsive ping frame may be verified by using alength/type field of the frame header.

When an inputted frame is the distance measurement frame that is theresult of a verification in the above operation, the inputted frame isforwarded to a next node with a top priority. More specifically, whenthe output port does not transmit a frame and is in an idle state, thedistance measurement frame is immediately forwarded. When there is aframe already being transmitted via the output port, the frame alreadybeing transmitted is buffered and the distance measurement frame ispreferentially forwarded.

To precisely measure a distance between nodes on a network regardless ofa traffic state of the network, it is required to specially manage thedistance measurement frame. Accordingly, in an example embodiment, asdescribed above, the distance measurement frame has a higher prioritythan other frames and may preempt transmission resources of the otherframes, thereby providing a precise distance measurement result.

Also, the bridge apparatus receiving a ping frame compares a destinationaddress included in the frame header with an Ethernet address of thebridge apparatus and generates and transmits a responsive ping frame toa source address transmitting the ping frame when the two addresses areidentical with each other. When the two addresses are not identical witheach other, since the ping frame is not destined for the bridgeapparatus, the bridge apparatus forwards the ping frame to a next node.

For reference, a sender may include a service provider including a mediaserver and a receiver may include a service receiver including a mediaplayer. The service receiver may be a bridge apparatus included in alocal Ethernet network supporting a residential Ethernet.

The Ethernet frame transmission method according to an exampleembodiment may be embodied as a program instruction capable of beingexecuted via various computer units and may be recorded in acomputer-readable recording medium. The computer-readable medium mayinclude a program instruction, a data file, and a data structure,separately or cooperatively. The program instructions and the media maybe those specially designed and constructed for the purposes of anexample embodiment, or they may be of the kind well-known and availableto those skilled in the art of computer software arts. Examples of thecomputer-readable media include magnetic media (e.g., hard disks, floppydisks, and magnetic tapes), optical media (e.g., CD-ROMs or DVD),magneto-optical media (e.g., optical disks), and hardware devices (e.g.,ROMs, RAMs, or flash memories, etc.) that are specially configured tostore and perform program instructions. The media may also betransmission media such as optical or metallic lines, wave guides, etc.including a carrier wave transmitting signals specifying the programinstructions, data structures, etc. Examples of the program instructionsinclude both machine code, such as produced by a compiler, and filescontaining high-level language codes that may be executed by thecomputer using an interpreter. The hardware elements above may beconfigured to act as one or more software modules for implementing theoperations of example embodiments.

An aspect of an example embodiment is applied to a network bridgeapparatus operating according to the above Ethernet frame transmissionmethod. FIG. 5 is a block diagram illustrating an internal configurationof a network bridge apparatus according to an example embodiment.

Referring to FIG. 5, a frame receiving unit 510 receives an Ethernetframe 501 from a previous node. In detail, the frame receiving unit 510receives a frame header first and an HCRCF and HCRC located in the frontof a frame payload. Data 511 such as the frame header, the HCRCF, andthe HCRC is inputted to a CRC unit 520.

The CRC unit 520 performs a CRC on the frame header by using the HCRCFand the HCRC or performs a CRC on an entire Ethernet frame 501 by usinga CRC field of the received Ethernet frame 501. Thus, depending uponcircumstances, the CRC unit 520 outputs a result of the CRC on the frameheader or outputs a result of the CRC on the frame via path 521. Theresults of the CRC are inputted to a state management unit 530.

The state management unit 530 determines a state of operation accordingto the results of the CRC. In detail, since the state management unit530 manages the apparatus by dividing the state of operation into aplurality of states, the apparatus may operate as a finite statemachine.

FIG. 6 is a diagram illustrating transitions between states maintainedand determined by the state management unit 530. Referring to FIG. 6,the state of the apparatus includes a first state 610 and a second state620. The first state 610 indicates a state when a previous node isdetermined to support the check-and-forward technique. The second state620 indicates a state when the previous node is determined not tosupport the check-and-forward technique.

Namely, in the network bridge apparatus, the previous node and a nextnode connected to the apparatus may vary with a change in a physicalconnection state and a routing path. Accordingly, the network bridgeapparatus does not maintain whether the previous node and the next nodesupport the check-and-forward technique, as a fixed value but has todynamically determine whether the previous node and the next nodesupport the check-and-forward technique every time by using an Ethernetframe received from the nodes.

Accordingly, the state management unit 530 determines a case in whichthe previous node is determined to support the check-and-forwardtechnique and a case in which the previous node is determined not tosupport the check-and-forward technique, to be the first state 610 andthe second state 620, respectively. When determination with respect towhether the previous node supports the check-and-forward technique ischanged, a state transition is performed. An operation of forwarding theEthernet frame is performed differently depending upon the state,thereby flexibly performing a coupling with a conventional Ethernetbridge apparatus or a network bridge apparatus according to anotherexample embodiment.

For this, the state management unit 530 maintains or changes a firstcounter variable M determining whether to perform a transition from thefirst state 610 to the second state 620 and a second counter variable Ndetermining whether to perform a transition from the second state 620 tothe first state 610. As described above, the state management unit 530accumulates an event that becomes a basis for a state transition andperforms a state transition when a result of the accumulation arrives ata threshold. By using the counter variables, when the threshold issuitably selected, optimizing operations of the network bridge apparatusmay be more precisely controlled. In FIG. 6, when values of the firstcounter variable M and the second counter variable N arrive at certainthreshold such as 3 and 7,respectively, a state transition is performed.Though not shown, to apply the above threshold, it is required toinitialize the first counter variable M and the second counter variableN. The basis for selecting the threshold will be described in detaillater.

For reference, in the present specification, for the convenience of thedescription, the state management unit 530 determines only whether theprevious node supports the check-and-forward technique. However, asdescribed above, since an Ethernet frame is bidirectionally transmittedvia input and output ports of the network bridge apparatus, the statemanagement unit 530 may determine whether the next node supports thecheck-and-forward technique, as well as the previous node, and maymanage a result of the determination as the state.

Referring back to FIG. 5, the network bridge apparatus includes a frametransmission unit 540 that discards or transmits the received Ethernetframe to the next node by referring to the result of the CRC on theheader and the frame, performed by the CRC unit 520, and the statemanagement unit 530 determining the state. For this, the frametransmission unit 540 receives a frame 512 from the frame receiving unit510. The frame transmission unit 540 communicates with the CRC unit 520via 522 and 541 and communicates with the state management unit 530 via531. Further, frame transmission unit 540 outputs Ethernet frame 502.

FIG. 7 is a flowchart illustrating operations of the frame transmissionunit 540, distinguished according to the state, for determining whethera HCRCF is valid, and a value of the HCRCF. In operation S710, the frametransmission unit 540 determines if the state of operation is the firststate or the second state. If the state of operation is the first state,the frame transmission unit 540 determines, in operation S720, if theHCRCF is valid or invalid. The operations for the HCRCF being invalidare illustrated in FIG. 10. However, if HCRCF is valid, the frametransmission unit 540 determines, in operation S730, if the HCRCF is ONor OFF. The operations for the HCRCF being OFF are illustrated in FIG. 9and the operations for the HCRCF being ON are illustrated in FIG. 8.Returning to operation S710, if the state of operation is the secondstate, the frame transmission unit 540 determines, in operation S740, ifthe HCRCF is valid or invalid. The operations for the HCRCF beinginvalid are illustrated in FIG. 12 and the operations for the HCRCFbeing valid are illustrated in FIG. 11. The operations of the frametransmission unit 540 with respect to the distinguished cases shown inFIG. 7 are illustrated in FIGS. 8 through 12.

For reference, the HCRCF may be expressed via a plurality of bits. Forexample, when using 8 bits, a binary number “10101011” may be used fordesignating “on” and a binary number “01010100” may be used fordesignating “off”. When the received HCRCF includes another bit streamin addition to the above two, the HCRCF is invalid and therefore a valueof the HCRCF may not be determined to be “on” or “off”.

FIG. 8 is a flowchart illustrating operations when the frametransmission unit 540 transmits an Ethernet frame whose HCRC value is ONin the first state 610 as determined in operation S730 of FIG. 7. In thefirst state 610 it may be expected that an inputted frame includes avalid HCRCF because a previous node supports the check-and-forwardtechnique. In operation S810, a CRC on the frame header is determinedand is performed by the CRC unit 520. When there is no error in a frameheader as determined by a CRC on the frame header and since a framedesired by the first state 610 is received, the state management unit530 does not change a state. Also, since the above result of the CRCbecomes a strong basis for maintaining a present state, the statemanagement unit 530 initializes a first state transition countervariable (M) for the first state 610, associated with the transition tothe second state 620, as 0 in operation S820. The state management unit530 then enables the frame transmission unit 540 to forward the frame toa next node in operation S830.

On the other hand, when there is an error in the frame header asdetermined in operation S820 based on the result of the CRC, a CRC onthe entire frame is performed in operation S850 and a result of the CRCis evaluated in operation S860. When there is no CRC error in the frame,the state management unit 530 transitions the state of the networkbridge apparatus to the second state 620 in operation S870 and thenenables the frame transmission unit 540 to forward the frame inoperation S840. Here, despite the previous node having transmitted ageneral Ethernet frame not including an HCRCF and HCRC, the HCRCF has avalue identical with a valid bit stream by a mere chance. When there isCRC error in the frame, the frame is discarded in operation S880.

FIG. 9 is a flowchart illustrating operations when the frametransmission unit 540 transmits an Ethernet frame whose HCRC value isOFF in the first state 610 as determined in operation S730 of FIG. 7. Inthis case, since there is a node not supporting the check-and-forwardtechnique in a network path, the check-and-forward function cannot beused on the entire end-to-end path. In this case, the CRC unit 520 doesnot separately perform a CRC on a frame header and only performs a CRCon the entire frame in operation S910. A result of the CRC is evaluatedin operation S920.

When there is no CRC error in the frame as determined in operation S920based on the result of the CRC, and since the present state ismaintained, the state management unit 530 initializes a value of thefirst state transition counter variable (M) to be 0 in operation S930.The frame transmission unit 540 then forwards the frame to a next nodein operation S940. However, when there is a CRC error in the frame, asdetermined in operation S920, the state management unit 530 discards theframe in operation S950.

FIG. 10 is a flowchart illustrating operations when the frametransmission unit 540 transmits an Ethernet frame including an invalidHCRCF in the first state 610 as determined in operation S720 of FIG. 7.When the HCRC is invalid, the CRC unit 520 performs CRC on an entireframe in operation S1010 and a result of the CRC is evaluate inoperation S1020. When there is a CRC error in the frame, the frame isdiscarded in operation S1070. However, when there is no CRC error in theframe, the frame may be determined to be valid and does not include aHCRCF and HCRC. Accordingly, the state management unit 530 increases avalue of the first state transition counter variable (M) by 1 inoperation S1030. In operation S104 o it is determined if the first statetransition counter M is equal to or greater than 3. When the first statetransition counter M is three or greater the state management unit 530performs a transition to the second state 620 in operation S1050. Afterthe transition to the second state 620 or a determination that M is lessthan 3, the frame transmission unit 540 then performs an operation offorwarding in operation S1060.

FIG. 11 is a flowchart illustrating operations when the frametransmission unit 540 transmits an Ethernet frame including a validHCRCF in the second state 620 as determined in operation S740 of FIG. 7.As shown in FIG. 11, in this case, the state management unit 530 mayperform a CRC on a frame header in operation S1110 and evaluate a resultof the CRC in operation S1115.

When there is CRC error in the frame header, the state management unit530 may perform a CRC on the frame in operation S1155 and the result isevaluated in operation S1160. If there is a CRC error in the frame, theframe is discarded in operation S1150. However, if there is no CRCerror, a value of a second state transition counter variable (N) is setto 0 in operation S1165, thereby maintaining the current state. Theframe transmission unit 540 then performs an operation of forwarding inoperation S1145.

When there is no CRC error in the frame header, the state managementunit 530 may perform a CRC on the frame in operation S1120 and theresult is evaluated in operation S1125. If there is a CRC error in theframe, the frame is discarded in operation S1150. Here, the value of thesecond state transition counter variable (N) is not changed by the statemanagement unit 530. If there is no CRC error in the frame, the frame isdiscarded in operation S1150 the value of a second state transitioncounter variable (N) is increased by 1 in operation S1130 to perform atransition to the first state 610. When the second state transitioncounter variable (N) becomes 7 as determined in operation S1135, thestate management unit 530 performs a state transition of the networkbridge apparatus to the first state 610 in operation S1140 and the frametransmission unit 540 performs an operation of forwarding in operationS145 that is suitable for the state transition. However, if the secondstate transition counter variable (N) is less than 7 in operation S1135,the frame transmission unit 540 performs an operation of forwarding inoperation S1145.

FIG. 12 is a flowchart illustrating operations when the frametransmission unit 540 transmits an Ethernet frame including an invalidHCRCF in the second state 620 as determined in operation S740 of FIG. 7.In this case, the CRC unit 520 performs a CRC on the entire frame inoperation S1210 and evaluates a result of the CRC in operation S1220.When there is no CRC error in the entire, the state management unit 530initializes a value of the second state transition counter variable (N)to be 0 in operation S1230. Thereby the current state is maintained.Accordingly, the frame transmission unit 540 forwards the frame inoperation S1240. However, when there is a CRC error in the frame, theframe transmission unit 540 discards the frame in operation S1250.

In the operations of the frame transmission unit 540, describedreferring to FIGS. 7 through 12, the operation of forwarding a frame isperformed differently depending upon the states of a previous node and anext node. Namely, when the states of the previous node and the nextnode are the first state 610, the frame transmission unit 540 transmitsthe frame as is to the next node. Conversely, when the state of the nextnode is the second state 620, the frame transmission unit 540 removes aHCRCF and HCRC of the received frame and transmits the frame to the nextnode. Also, when the state of the previous node is the second state 620and the state of the next node is the first state 610, the frametransmission unit 540 inserts an HCRCF in the received frame,establishes a value of the inserted HCRCF to be “off”, and transmits theframe to the next node.

According to the above example embodiment, the threshold associated witha transition of the state is determined to be not less than 3, withrespect to a transition from the first state 610 to the second state620. The threshold is determined to be not less than 7, with respect toa transition from the second state 620 to the first state 610. The abovethreshold is determined based on a probability computation result asfollows.

It is assumed that a Poisson error whose bit error rate (BER) is 10⁻⁸,regardless of whether there is an error in one bit of a HCRCF withrespect to 3 sequential frames. A probability of a transition to thesecond state is computed as (8×10⁻⁸)³=5.12×10⁻²². In a worst case,specifically, with respect to a minimized frame of 512 bits in anultrahigh speed Ethernet network environment, the above BER indicates anincorrect state transition occurs once in 512×10⁻¹⁰/5.12×10⁻²²=10¹⁴s=3×10 ⁻⁶ years. Accordingly, when the threshold ofthe state transition from the first state 610 to the second state 620 isdetermined to be not more than 3, a stable function may be secured.

Next, a minimized threshold 7 associated with the transition from thesecond state 620 to the first state 610 will be described. When assumingthat frame data includes a random bit pattern, a probability of an errorin the transition may be computed as 2⁻⁵⁶=1.39×10⁻¹⁷. In a worst case,the BER indicates an incorrect state transition occurs once in512×10⁻¹⁰/1.39×10⁻¹⁷=117 years. Accordingly, the threshold of the statetransition from the second state 620 to the first state 610 isdetermined to be not less than 7, thereby providing a stable function.

A network bridge apparatus according to another example embodiment mayfurther include a distance measurement frame verification unit (notshown) verifying whether an Ethernet frame is a distance measurementframe. The distance measurement frame verification unit may verifywhether the received frame is transmitted to measure a network distance,by using a length/type field of a frame header of the received frame.

When the received frame is the distance measurement frame as a result ofa verification performed by the distance measurement frame verificationunit, the frame transmission unit 540 forwards the distance measurementframe with a top priority. For this, the network bridge apparatusaccording to the present example embodiment includes a frame buffer.Namely, with respect to the Ethernet frame determined to be the distancemeasurement frame, the frame transmission unit 540 verifies whether anoutput port is an idle state, immediately forwards the distancemeasurement frame when the output port is the idle state, temporarilystores a frame currently being transmitted in the frame buffer when theframe is currently being transmitted via the output port, andpreferentially transmits the distance measurement frame.

Hitherto, referring to FIGS. 5 through 12, the network bridge apparatusaccording to an example embodiment has been described. Since detailedcontents of the example embodiments described referring to FIGS. 1through 4 can be applied to the network bridge apparatus according to anexample embodiment, hereinafter, description of detailed contentsassociated with the network bridge apparatus will be omitted.

An aspect of example embodiments also provides a frame transmissionmethod capable of satisfying a requirement for reduced time delayrequired in a real-time application, by securing precision of data of anEthernet frame header via a CRC header using a header CRC flag includedin the Ethernet frame and a header CRC as well as selectively performingCRC on an entire Ethernet frame.

According to an aspect of example embodiments, a function of preciselymeasuring a distance between a content provider and a content receiveron a network is also supported by forwarding a distance measurementframe with a top priority. Accordingly, digital rights management (DRM)with respect to contents provided in real-time may be effectivelysupported.

According to an aspect of example embodiments, an additional functionassociated with real-time applications is also effectively supported.Further, compatibility with a conventional Ethernet bridge apparatus ismaintained. Also, via this, flexibility and expandability of an Ethernetnetwork may be secured in a residential Ethernet.

According to an aspect of example embodiments, in embodying the networkbridge apparatus, a state transition counter is compared with athreshold determined by probability computation to perform a transitionof a state, thereby more precisely forwarding a frame.

A number of examples have been described above. Nevertheless, it will beunderstood that various modifications may be made. For example, suitableresults may be achieved if the described techniques are performed in adifferent order and/or if components in a described system,architecture, device, or circuit are combined in a different mannerand/or replaced or supplemented by other components or theirequivalents. Accordingly, other implementations are within the scope ofthe following claims.

1. A method of transmitting an Ethernet frame via a network bridge, themethod comprising: receiving the Ethernet frame from a previous node;verifying whether the Ethernet frame is a distance measurement frame formeasuring a network distance between a sender and a receiver, byreferring to a header of the Ethernet frame; and forwarding the distancemeasurement frame with a top priority when the Ethernet frame isverified to be the distance measurement frame as a result of theverification.
 2. The method of claim 1, wherein the forwarding thedistance measurement frame comprises buffering the Ethernet frame beingcurrently transmitted and preferentially forwarding the distancemeasurement frame, when an Ethernet frame being currently transmitted toa next node exists.
 3. The method of claim 1, wherein the forwarding thedistance measurement frame comprises forwarding the distance measurementframe to a source address of the distance measurement frame when anaddress of the network bridge is identical with a destination address ofthe distance measurement frame.
 4. The method of claim 1, wherein thedistance measurement frame comprises at least one of a ping frametransmitted from a service provider to a service receiver and aresponsive ping frame transmitted from the service receiver to theservice provider in response to the ping frame.
 5. The method of claim4, wherein the service provider comprises a media server and the servicereceiver comprises a media player.
 6. The method of claim 1, wherein theEthernet frame supports residential Ethernet.
 7. A computer-readablerecording medium in which a program for executing a method oftransmitting an Ethernet frame via a network bridge is recorded,comprising: receiving the Ethernet frame from a previous node; verifyingwhether the Ethernet frame is a distance measurement frame for measuringa network distance between a sender and a receiver, by referring to aheader of the Ethernet frame; and forwarding the distance measurementframe with a top priority when the Ethernet frame is verified to be thedistance measurement frame as a result of the verification.